It was very easy to assume that the doors of Star Trek (in all incarnations) were automated. After all, here in the boring, non-futuristic gift, we experience automatic doors in the most common places like gas stations, shopping malls and the like. Although they are not as common in the 1960s as today, automatic doors like those we know were invented in 1954 and the first commercially available automated door was installed in 1960.
However, although the technology existed at the time the exhibition was created (and certainly in all subsequent additions to the franchise like Star Trek: The Next Generation ), the doors on the sets have always been manually opened by the stage crew. In the 1996 book Inside Star Trek: The Real Story written by Herbert F. Solow and Robert H. Justman, Solow-Desilus Executive Leader of Production for the Original Star Trek-explained how it worked: [ Superior hand-eye coordination was necessary for brain surgeons, prestigilators and the guy responsible for opening the various doors on the set. He accomplished it by standing out of sight of the camera and driving the "mechanisms". The mechanisms consisted of wires attached to the door's sides and were made through a series of pulleys. The deputy director, who stands behind camera and watched the scene, would trigger a red light cued offstage the guy had the moment to open the doors. He should yank on the headline. This enabled the threads that ran through the pulleys and opened the doors just in time for Kirk or Spock to come in or out.
Mechanisms always worked; The managers were not as reliable. Sometimes cue would be given too early, and the doors would open long before the actors reached them. This "magic door" syndrome usually gave an enthusiastic laugh from everyone except, perhaps, the director, who was usually behind the schedule. For him, it was not funny.
Sometimes cue would be given too late and the actors who rely on souls as they were sometimes bounced off the unopened doors. This almost always took an enthusiastic laugh, especially from the director. De Kelley became overheated to remark: "You can be killed to go to the cafe aboard this ultra-modern space cruiser."
Later when a builder in Santa Barbara, California wrote to us, asked for ideas on how to build sliding doors that work as fast as they boarded the company, my recommendation to Bob was to tell the builder that he would get another deputy director and a faster offstage guy.
The mechanism did not change much over the years, and you can find "Star Trek Door Bloopers" on YouTube that show actors from the franchise that enter the doors throughout the decades. The franchise has existed.
Image courtesy of Paramount Pictures.